In recent years, harmful substance emission in the process of painting and plating in the forming of vehicle components has been restricted more tightly from an environmental point of view. Accordingly, in particular, acrylic decoration films and protection films have been attracting attention as alternatives to such substances and for use in protecting the components. These protection films and decoration films are used in such a manner that the films are adhered to the surface of a base material. Therefore, such a film is required to have sufficient transparency to allow printing and patterns on the surface of the base material to be clearly visible, and is also required to have flex cracking resistance during insert molding or in-mold forming.
Moreover, since the film itself is printed, the film is required to have chemical resistance, and in addition, the film needs to have stain resistance to lactic acid components contained in human sebum and sweat and to sunscreens, for example, Coppertone (registered trademark), used on human skin during the summer season and in a hot region, because vehicle interior components frequently come into contact with human hands, and there are increasing cases of base material degradation that occurs when the aforementioned lactic acid components and/or sunscreens adhere to the vehicle interior components.
As films that satisfy these quality requirements, a multilayer film produced by coextrusion molding of a methacrylic resin composition with a fluororesin that is excellent in terms of weatherability and chemical resistance, and an acrylic resin film having a surface hard-coated with a fluororesin, have been drawing strong attention in the market. In particular, the following method is attracting strong attention, in which: a film obtained by laminating a vinylidene fluoride-based resin, which is a melt-moldable fluororesin, on an acrylic resin is used as decoration on the surface of a plastic molded article so as to serve as an alternative to painting on the surface.
However, a vinylidene fluoride-based resin is a crystalline resin, and has a high crystallization speed. For this reason, achieving satisfactory transparency with such a vinylidene fluoride-based resin is highly difficult. In view of this, thinning of the film (see Patent Literature 1), mixing of a vinylidene fluoride resin with a methacryl resin (see Patent Literature 2), control of molding conditions in film processing (extrusion molding temperature, discharge rate, and residence time in an extruder) (see Patent Literature 3), etc., have been proposed. However, it is difficult to achieve required transparency with these methods.
In addition, with vinylidene fluoride resins, it is also difficult to realize surface strength desired for the aforementioned use.
Consideration has also been given to a method of obtaining a vinylidene fluoride resin film that is excellent in terms of transparency and surface smoothness by sandwiching a vinylidene fluoride resin with metal rolls adjusted to have a suitable temperature (see Patent Literature 4). However, in the case of adopting such a method, due to increase in processing steps, installation of new equipment or modification of existing equipment may become necessary, which is economically disadvantageous. Therefore, a method that makes it possible to produce a vinylidene fluoride resin film in a simpler manner is desired.
If a fluorine-containing alkyl (meth)acrylate-based resin is formed into a film by extrusion molding, die lines occur due to resin deposit that is caused by thermal decomposition of the resin. This causes a difficulty in stable film production (see Patent Literatures 5 and 6).
In one method, a hard coating layer, and an antireflection layer made of a fluorine-containing and alkyl-group-containing (meth)acrylate, are sequentially laminated on a base film by wet coating, which causes no thermal degradation (see Patent Literature 7). However, applying this method to insert molding or in-mold forming is difficult, because the hard coating layer is three-dimensionally crosslinked and it is difficult to perform vacuum molding of the hard coating layer.